Retina’s Layers, Eye’s Blood Vessels May Distinguish NMOSD From MS
Examining the thickness of certain retinal layers in the eye, along with structural changes in the eyes’ blood vessels, can help differentiate neuromyelitis optica spectrum disorder (NMOSD) from multiple sclerosis (MS), a study found.
Overall, two particular retinal layers — the peripapillary retinal nerve fiber layer (pRNFL) and the macular ganglion cell-inner plexiform layer (GC-IPL) — were thinner, and vessel density and blood perfusion in the macula, another retinal layer, was lesser in people with NMOSD than those with MS, its researchers reported.
The distinct retinal structure and small blood vessel characteristics evident in these patients could potentially be used to diagnose NMOSD, which is frequently misdiagnosed as MS, they added.
NMOSD and MS, both autoimmune disorders, affect the central nervous system (the brain and spinal cord) and cause significant disability. Despite having distinct causes, they share a number of similarities that make an accurate diagnosis challenging.
Because the brain and the eye’s retina originate from the same structure in embryos and share their blood vessel supply, researchers are starting to see this structure as “an accurate window into the brain.”
In fact, multiple studies have demonstrated that changes in the thickness of some of the retina’s layers — particularly, pRNFL and GC-IPL — can help to evaluate neurodegeneration and the loss of brain volume in both MS and NMOSD. Studies into whether these measurements can be combined with an assessment of the eye’s blood vessel morphology to discriminate between these disorder, however, are lacking.
Of note, the retina can be examined with an advanced imaging technique called optical coherence tomography (OCT), while blood vessel structure requires a technique called OCT angiography.
Researchers at the Sun Yat-sen University, in China, investigated retinal layers and blood vessels in the eyes of 91 NMOSD patients with antibodies against the aquaporin-4 (AQP4) water channels, 83 MS patients, and 34 healthy people serving as controls.
Of the 135 eyes of NMOSD patients that were imaged, 90 (66.7%) had a history of optic neuritis (inflammation of the optic nerve), as did 76 of the 146 eyes (52%) of MS patients.
NMOSD patients had a median age of 41, MS patients of 31, and healthy controls of 27; most in all groups were female.
Overall, OCT results showed that both pRNFL and GC-IPL were significantly thinner in MS and NMOSD patients compared with controls. But the thickness of those layers was also significantly less in NMOSD patients than in people with MS.
These differences were independent of the presence of optic neuritis, one of the main symptoms of NMOSD.
Regarding blood vessel structure, NMOSD patients showed a smaller vascular density in five of eight regions of the macula, and a smaller perfusion density (the area occupied by blood vessels) in four of those regions than did MS patients. Again, the results were not affected by optic neuritis, the team noted.
In both patient groups, the two blood vessel measures were significantly associated with the thickness of both retinal layers.
Statistical analyses also found that a combination of all four measures — pRNFL thickness and GC-IPL thickness plus vascular density, and perfusion of certain regions in the macula — was best for discriminating between these two disorders, with an accuracy of 83.3%.
“Our study indicated that the patterns and severity of macular structure and microvasculature loss differed significantly between MS and NMOSD,” the investigators wrote.
“Combining [OCT angiography] and OCT may yield promising diagnostic properties in distinguishing both diseases,” as the two imaging techniques used together “had a better discrimination ability than OCT alone,” they concluded. “Further clinical trials are warranted to assess the potential implications of the retinal vascular parameters for the diagnosis and assessment of these disorders.”